Sleep problems, based on mother's reports, were examined in children of bipolar, unipolar, and well mothers. Mothers' reports were obtained twice on two of their children at an interval of approximately three years: on the younger children when they were between 2 and 3 1/2 years old and again when they were between 5 and 6 1/2 years old; on the older children when they were between 5 and 8 years old and again when they were between 8 and 11 years old. Children's sleep problems also were examined in relation to family diagnosis (incidence of parental affective illness in families with psychiatric data available for both parents); i.e., in children with two affectively ill parents, children with one affectively ill parent, and children with well parents.